Glypican-3 (GPC3) is an oncofetal antigen that belongs to the glypican family of glycosyl-phosphatidylinositol-anchored heparin sulfate proteoglycans. Glypicans are characterized by a covalent linkage to complex polysaccharide chains called heparinsulphate glycosaminoglycans. Glypicans are involved in cell signaling at the cellular-extracellular matrix interface. (Sasisekharan et al., Nat. Rev. Cancer 2:521-528 (2002).) To date, six distinct members of the human glypican family have been identified. Cell membrane-bound GPC3 is composed of two subunits, linked by one or more disulfide bonds.
GPC3 is expressed in fetal liver and placenta during development and is down-regulated or silenced in normal adult tissues. Mutations and depletions in the GPC3 gene are responsible for the Simpson-Golabi-Behmel or Simpson dysmorphia syndrome in humans. GPC3 is expressed in various cancers and, in particular, hepatocellular carcinoma (“HCC”), melanoma, Wilm's tumor, and hepatoblastoma. (Jakubovic and Jothy, Ex. Mol. Path. 82:184-189 (2007); Nakatsura and Nishimura, Biodrugs 19(2):71-77 (2005).)
HCC is the third leading cause of cancer-related deaths worldwide. Each year, HCC accounts for about 1 million deaths. (Nakatsura and Nishimura, Biodrugs 19(2):71-77 (2005).) Hepatitis B virus, hepatitis C virus, and chronic heavy alcohol use leading to cirrhosis of the liver remain the most common causes of HCC. The incidence of HCC has increased dramatically in the United States, in part becausebecause of the spread of the hepatitis C virus. HCC is treated primarily by liver transplantation or tumor resection. Patient prognosis is dependent on both the underlying liver function and the stage at which the tumor is diagnosed. (Parikh and Hyman, Am J Med. 120(3):194-202 (2007).) Effective strategies for the treatment of HCC and other tumors expressing GPC3 are needed. It would thus be desirable to have available means and methods for targeting GPC3, preferably GPC3 expressed on tumor cells.
International Patent Application No. PCT/EP2011/070119 disclosed lipocalin muteins, derived from human lipocalin 2 (also called human neutrophil gelatinase-associated lipocalin (hNGAL)), which are capable of binding GPC3. The present disclosure, however, provides additional GPC3-binding proteins having advanced features attendant to these proteins.